[2pt] Add a check in `ras2inundation.py` to ensure the flow file is built correctly

[ar-siddiqui]

When using 2024 04 05 outputs from RAS2FIM and the ras2inundation.py script and conda environment from latest dev branch (6584be0). The following error is encountered

TypeError: Cannot index by location index with a non-integer key

Details:

================================================================= 
          RUN Inundation tool
  (-g): geocurves directory D:\Users\abdul.siddiqui\workbench\projects\ras2fim_demo\20240405\final\geo_rating_curves
  (-f): flow file D:\Users\abdul.siddiqui\workbench\projects\ripple_1d_outputs\flows_harvey.csv
  (-t): output inundation gkpg D:\Users\abdul.siddiqui\workbench\projects\ras2fim_demo\20220508\inundation\harvey.gpkg
 --- Start: 05/08/2024 18:18:44 (UTC time)
=================================================================

Completed creating a dictionary of available feature_ids and geocurve files. 
Derived ras2fim version v2.0.2.0 from geocurve files. 
Compiling feature_ids info (discharge, stage, geometry) ...  
 2024-05-08 18:18:58 <CRITICAL> : Traceback (most recent call last):
  File "ras2inundation.py", line 244, in <module>
    produce_inundation_from_geocurves(**args)
  File "ras2inundation.py", line 131, in produce_inundation_from_geocurves
    subset_geocurve = geocurve_df.iloc[row_idx]
  File "D:\Users\abdul.siddiqui\AppData\Local\anaconda3\envs\ras2fim\lib\site-packages\pandas\core\indexing.py", line 1103, in __getitem__
    return self._getitem_axis(maybe_callable, axis=axis)
  File "D:\Users\abdul.siddiqui\AppData\Local\anaconda3\envs\ras2fim\lib\site-packages\pandas\core\indexing.py", line 1653, in _getitem_axis
    raise TypeError("Cannot index by location index with a non-integer key")
TypeError: Cannot index by location index with a non-integer key